1. Field of the Invention
The present invention relates to a parallel circuit structure and, more particularly, to a board-mounted parallel circuit structure with efficient power utilization.
2. Description of the Related Art
Regular circuit structures in lighting applications mostly pertain to circuit structure of a single substrate. The circuit structure is normally fabricated on a single substrate. In view of the positive and negative power terminals of a single substrate all formed on an identical plane, different voltages vary from location to location at wires depending on how far the distance from the measured point to the positive or negative terminal is. The farther the measured point is away from the power source is, the higher the resistance value is measured at the point. While the resistance value to a measured point on the circuit structure increases, a resulting voltage drop to the measured point also increases to cause lower luminance of a lighting module, such as an LED (Light-emitting Diode), and to cause worse power utilization efficiency.
Conventional types of driving circuits for lighting include a parallel circuit, a series circuit and a compound circuit. With reference to FIG. 3, a conventional parallel circuit for a lighting driving circuit is connected in series between the positive and negative electrodes of a power supply and has multiple light-emitting modules connected in parallel to each other. Each light-emitting module is composed of a circuit loop including a light-emitting diode (LED) 91 and a resistor R. With reference to FIG. 4, multiple series circuits and a compound circuit are illustrated. The series circuit includes multiple LEDs 91 connected in series to each other. The compound circuit is formed by connecting the multiple series circuits .in parallel to each other, and is connected between the positive and negative electrodes of a power supply.
A conventional AC (Alternating Current) driven LED circuit includes a full-wave rectifier, a compensation module, an LED module and a lighting efficiency enhancing module. The full-wave rectifier has at least four LED units arranged in the form of a full bridge to provide two output terminals. The compensation module has four compensation capacitors connected in parallel between two terminals of each LED unit. The LED module is connected to the two output terminals of the full-wave rectifier, and includes an LED string having multiple LEDs connected in series to each other. The lighting efficiency enhancing module includes at least one capacitor connected in parallel between two terminals of the LED module.
As can be seen from the foregoing technique, the wiring length on a single substrate certainly affects lighting luminance and power utilization efficiency, and each light-emitting module of the parallel circuit needs to be connected in parallel to a resistor R to limit current. However, the drawbacks of the parallel circuit reside in high cost and overheating issues because of high operating voltage. The series circuit and the compound circuit also need to boost voltage for all the LEDs to have the same luminance and thus consume more power. Especially when one of the LEDs 91 fails and an open circuit is caused, all other LEDs 91 in the same LED string become not operable. Although the use of the compensation module and the lighting efficiency enhancing module can increase luminance, efficiently utilize power, and lower the risk of LED damage, higher cost still arises from the additional compensation module and the lighting efficiency enhancing module, thus failing to ensure cost-effectiveness to manufacturers in the related industry.